Sun Requirement: Onions require full sun - the more the better! Avoid growing onions next to crops that might shade your onions.
Soil Fertility: Onions prefer soil with a pH between 6.2 and 6.8. If your soil is too acid, add ground limestone; if it is too alkaline, add peat moss. Added compost or a balanced organic fertilizer is needed to grow big, mild onions if your soil fertility is low. For the best growth and yield, onions need fertilizer at planting time and additional side dressing. (See "Planting" and "Fertilizing" below.)
Planting: Onions grow best on raised beds or raised rows at least 4" high and 20" wide. Plant your onions 4 to 6 weeks before the last estimated spring freeze.